The compound 4-hydroxystyrene is a well-known compound which is useful as a food flavoring substance and as an intermediate in the preparation of polymers and copolymers utilized in the manufacture of coatings, electronic components, ion exchange resins, photoresists, etc. Although there are several known methods of preparing 4-hydroxystyrene, those methods are not commercially feasible in the further utilization of 4-hydroxystyrene, such as, for example, for use in the preparation of a photoresist intermediate such as 4-tertiarybutoxycarbonyloxystyrene. The reason for this is that the 4-hydroxystyrene is difficult to 4-solate because it readily polymerizes and decomposes and is toxic via &kin absorption. A preparation for 4-hydroxystyrene utilizing 4-acetoxystyrene is reported in a paper entitled "Preparation of Vinylphenols and Isopropenylphenols", Corson et al., Volume 23, April 1958 J. Org. Chem. In that preparation, 4-acetoxystyrene is saponified in an aqueous system with a large concentration of a soluble base, KOH, to produce an aqueous solution of the potassium salt of 4-hydroxystyrene which is neutralized with acid to precipitate 4-hydroxystyrene. The procedure is not practical or commercially feasible for production of large quantities of 4-hydroxystyrene because the 4-hydroxystyrene is not stable and readily polymerizes under the aqueous saponification conditions employed therein which involve high concentrations of soluble base. A more efficient process for producing 4-hydroxystyrene from 4-acetoxystyrene is desired and needed. The present invention provides a method wherein excessive polymerization of the 4-acetoxystyrene and/or the 4-hydroxystyrene in the formation of 4-hydroxystyrene is avoided.
The compound 4-tertiary-butoxycarbonyloxystyrene is useful as an intermediate in the production of the photoresist material poly(4-tertiary-butoxycarbonyloxystyrene). A route to 4-tertiarybutoxycarbonyloxystyrene is reported by Frechet et al., Polymer, 1983, 995 and Ito et al., U.S. Pat. No. 4,491,628, which involves a Wittig reaction starting with p-hydroxybenzaldehyde.
U.S. Pat. No. 5,082,965 also discloses a process for the preparation of alkoxycarbonyloxystyrene. Acyloxystyrene is reacted with a strong base in an aqueous medium to yield a phenolate. An alkoxycarbonylating agent is then added in an organic solvent and a phase transfer catalyst to yield the desired product.
The formation of 4-tertiarybutoxycarbonyloxystyren directly from p-hydroxystyrene has never been publicly reported, most likely due to the fact of the great instability of the 4-hydroxystyrene, as discussed above, and the difficulties most likely encountered thereby. These difficulties would lead one skilled in the art away from trying such synthesis using 4-hydroxystyrene even in the face of the synthesis of 4-tertiary-butoxycarbonyloxy-.alpha.-methylstyrene from 4-hydroxy-.alpha.-methylstyrene, as reported in U.S. Pat. No. 4,491,628. The reason for this is that .alpha.-methylstyrenes are much more stable to polymerization than unsubstituted styrenes such as 4-hydroxystyrene.
These and other objects and advantages of the present invention will become apparent from the following description.